use XML::LibXML;
my $dom = XML::LibXML->load_xml(IO => \*DATA);
foreach my $level ($dom->findnodes('//level | //levels'))
{
	printf("==== level '%s' ====\n", $level->getAttribute('name'));
	foreach my $child ($level->getChildrenByTagName('*'))
	{
		printf("contains %s '%s'\n", $child->nodeName, $child->getAttribute('name'));
	}
	print "\n";
}
__DATA__
<config>
     <levels name="a" target="29.6">
         <level name="b"    weight="50" target="35.1">    
             <study id="32" name="i"    weight="30" />
             <study id="36" name="j"    weight="70" />
         </level>
         
         <study id="37" name="k" weight="15" />
         
         <level name="c" weight="13" target="22.1">    
             <level name="d" weight="69.2">    
                 <level name="e"    weight="44.4">    
                     <study id="34" name="l"    weight="50" />
                     <study id="27" name="m"    weight="50" />
                 </level>
                 <level name="f"    weight="55.6">    
                     <study id="25" name="n"    weight="60" />
                     <study id="38" name="o"    weight="40" />
                 </level>
             </level>
             <level name="g" weight="30.8">    
                 <study id="50" name="p"        weight="75" />
                 <study id="70" name="q"        weight="25" />
             </level>
         </level>
         
         <level name="h" weight="22" target="19.0">    
             <study id="40" name="r"        weight="90.9" />
             <study id="22" name="s"        weight="9.1" />
         </level>
     </levels>
     
     <study id="19" name="t"        weight="0"    spec="p0f7=2" />
     <study id="19" name="u"        weight="0"    spec="p0f7=1" />
     <study id="62" name="v"        weight="0" />
</config>